# 2022 Redistricting for the House of Representatives Electoral Districts in Shizuoka Prefecture

## Redistricting Requirements

We incorporate as best as possible the rules that the Council on the House of Representatives Electoral Districts (hereafter “the commission”) follows by taking into account the following rules and practices:

1. The Act for Establishment of the Council on the House of Representatives Electoral Districts;
2. The guidelines adopted by the commission in the 2022 redistricting cycle; and
3. Other practices that the commission follows.

### 1. Act for Establishment of the Council on the House of Representatives Electoral Districts
According to the Act for Establishment of the Council on the House of Representatives Electoral Districts,

* The population ratio between the most populous and least populous districts in the country must not exceed two; and 
* “Circumstances such as administrative boundaries, geographical features, and transportation [routes]” must be taken into account.

### 2. Redistricting commission’s guidelines
According to the commission’s guidelines adopted in the 2022 redistricting cycle, known as the [policy for creating redistricting plans](https://www.soumu.go.jp/main_content/000794997.pdf),

* Districts must be contiguous;
* Municipalities must not be split in principle;
* Groups of towns and villages known as counties (*gun*) should not be split wherever possible; and 
* Natural and social conditions should be taken into account comprehensively

### 3. Redistricting commission’s practices
We follow the commission’s practices through:

* Only allowing municipalities to be split based on the boundaries of old municipalities that existed before 1999, wherever possible; and 
* Avoiding splitting municipalities into more than two districts. 

## Algorithmic Constraints

* We enforce a maximum population deviation of 15%.
* We add a constraint that penalizes municipality splits as well as a constraint that penalizes the splitting of municipalities into more than two districts.
* We also add a constraint to encourage the creation of geographically compact districts.

## Pre-processing Notes
* We remove the areas corresponding to 浜名湖 (Lake Hamana) from the Census shapefile.

## Simulation Notes

* We sample 40,000 districting plans across 4 independent runs of the Sequential Monte Carlo (SMC) algorithm.
* We do not allow municipalities to be split except for those that were split in the 2017 or 2022 map: 富士市 (Fuji-shi), 御前崎市 (Omaezaki-shi), and 伊豆の国市 (Izunokuni-shi). We allow these municipalities to be split along the boundaries of pre-merger municipalities. Note that the following municipalities were also split in the 2017 map: 静岡市葵区 (Aoi-ku, Shizuoka-shi), 静岡市駿河区 (Suruga-ku, Shizuoka-shi), 静岡市清水区 (Shimizu-ku, Shizuoka-shi), 浜松市中区 (Naka-ku, Hamamatsu-shi), 浜松市南区 (Minami-ku, Hamamatsu-shi), and 浜松市天竜区 (Tenryu-ku, Hamamatsu-shi). However, we do not allow these to be split in the simulation because the boundaries of the pre-merger municipalities do not necessarily match the boundaries of the wards that belong to Shizuoka City and Hamamatsu City.
* In addition, we do not allow counties (*gun*) to be split except for those that were split in the 2017 map. In the case of Shizuoka, we allow 駿東郡 (Sunto-gun) to be split along the boundaries of municipalities. 
* Finally, we remove plans with discontiguous districts as well as plans that split municipalities into three or more districts, after which we thin the sample to down to 5,000 plans.

## Data Sources

- [2020 Census](https://www.e-stat.go.jp/stat-search/files?page=1&toukei=00200521&tstat=000001136464&cycle=0&tclass1=000001136472)
- [2000 Census](https://www.e-stat.go.jp/gis/statmap-search?page=1&type=2&aggregateUnitForBoundary=A&toukeiCode=00200521&toukeiYear=2000&serveyId=A002005212000&coordsys=1&format=shape&datum=2000)
- [Periodical Ferry Route: National Geographic Information Download Service](https://nlftp.mlit.go.jp/ksj/gml/datalist/KsjTmplt-N09.html)
- [Lake and Ponds: National Geographic Information Download Service](https://nlftp.mlit.go.jp/ksj/gml/datalist/KsjTmplt-W09-v2_2.html)
- [Vote record of the House of Councilors election of July 21st 2019](https://www.soumu.go.jp/senkyo/senkyo_s/data/sangiin25/index.html)
- [Vote record of the House of Councilors election of July 10th 2022](https://www.soumu.go.jp/senkyo/senkyo_s/data/sangiin26/index.html)
